Cooling fan

ABSTRACT

A cooling fan includes a fan housing (10) having a central tube (14) extending upwardly therefrom, a bearing (30) received in the central tube, a stator (40) mounted around the central tube, and a rotor (20). The rotor includes a hub (22), a magnet (28) adhered to the hub, and a shaft (24) extending from the hub into the bearing. The stator includes a stator core (42) having a ring-shaped main body (420) and a plurality of claws extending radially and outwardly from the main body, coils (44) being wound on the claws, and a PCB (426) being electrically connected to the coils. At least one balancing structure (100) made of magnetizable material extends from the printed circuit board corresponding to a position between two adjacent claws of the stator core and exerts a downwardly attractive, magnetic force on the magnet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cooling fan, and more particularly relates to a cooling fan with a balancing structure for maintaining stable rotation of a rotor thereof.

2. Description of related art

With the continuing development of the electronic technology, electronic packages such as CPUs (central processing units) are generating more and more heat that requires immediate dissipation. Cooling fans are commonly used in combination with heat sinks for cooling the CPUs.

A conventional cooling fan includes a stator and a rotor having a hub with a plurality of fan blades extending therefrom. The stator establishes an alternating magnetic field interacting with the magnetic field of the rotor to drive the rotor to rotate. Thus rotation of the fan blades generates a forced airflow for cooling the electronic packages, such as the CPUs. The stator includes a bearing defining a bearing hole therein. The rotor has a shaft extending into the bearing hole and is thus rotatably supported by the bearing. However, during rotation of the rotor, the rotating fan blades generate an external pressure which pulls the rotor to move upwardly along the axial direction away from the stator, and the rotor is thus kept in a “floating” condition. The floating rotor is inclined to generate a level of noise, which can be unacceptable.

For the foregoing reasons, therefore, there is a need in the art for a cooling fan which overcomes the above-mentioned problems.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a cooling fan includes a fan housing having a central tube extending upwardly therefrom, a bearing received in the central tube, a stator mounted around the central tube, and a rotor. The rotor includes a hub, a magnet adhered to an inner side of the hub, and a shaft extending from a central portion of the hub into the bearing. The stator includes a stator core having a ring-shaped main body and a plurality of claws extending radially and outwardly from the main body, coils being wound on the claws, and a printed circuit board being electrically connected to the coils. At least one balancing structure extends from the printed circuit board corresponding to a position between two adjacent claws of the stator core. The at least one balancing structure is made of magnetizable material, and exerts a downwardly attractive, magnetic force on the magnet.

Other advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiments of the present invention with attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present cooling fan can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present cooling fan. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is an isometric, assembled view of a cooling fan in accordance with a preferred embodiment of the present invention;

FIG. 2 is an exploded view of the cooling fan of FIG. 1;

FIG. 3 is a cross-sectional view of the cooling fan taken along line Ill-Ill of FIG. 1; and

FIG. 4 is an enlarged, top view of a stator of the cooling fan of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 through 4, a cooling fan according to a preferred embodiment includes a fan housing 10, a balancing structure 100, a pair of bearings 30, a rotor 20, and a stator 40 in respective to which the rotor 20 is rotatable.

The fan housing 10 is square column shaped. An inner space (not labeled) is defined in the housing 10 receiving the rotor 20 and the stator 40 therein, and thus forms an air inlet 18 at a top side and an air outlet 16 at a bottom side of the housing 10. A base 12 is arranged in the inner space of the housing 10 at the bottom side thereof. A central tube 14 extends upwardly from a central portion of the base 12. The central tube 14 defines a central hole 140 therein. An annular recess 142 is respectively formed on an inner circumference of the top and bottom ends of the central tube 14 with an inner diameter larger than that of the central hole 140 of the central tube 14. The two recesses 142 communicate with the central hole 140.

The bearings 30 are respectively received in the recesses 142 of the central tube 14. In this embodiment, the bearings 30 are ball bearing which includes an annular inner ring, an annular outer ring and a plurality of balls sandwiched between the inner and outer rings. An outer diameter of the outer rings of the bearings 30 is substantially the same as the diameter of the recesses 142 of the central tube 14. It is to be understood that the bearings 30 are not limited to being ball bearings, other types of bearings, such as sleeve bearings, hydrodynamic bearings may also be adopted.

The rotor 20 includes a hub 22 forming a shaft seat 220 in a central portion thereof, a plurality of fan blades 26 extending radially from an outer periphery of the hub 22, a permanent magnet 28 adhered to an inner side of the hub 22, and a shaft 24 received in the shaft seat 220 and extending downwardly from a central portion of the shaft seat 220. A diameter of the shaft 24 is approximately the same as an inner diameter of the inner rings of the bearings 30 and thus the inner rings of the bearings 30 are fixedly mounted around the shaft 24 and rotate with the shaft 24. An annular notch (not labeled) is defined near a free end 240 of the shaft 24 far from the hub 22.

The stator 40 includes a stator core 42 consisting of layered yokes. Each yoke includes an annular main body 420 and four claws (not labeled) extending radially and outwardly from the main body 420. Alternatively, the stator core 42 may form more than or less than four claws according to practical needs. Each of the claws includes a linear-shaped portion 422 extending radially from the main body 420 and an arc-shaped portion 424 formed at an outer end of the linear-shaped portion 422. The arc-shaped portions 424 of the claws are concentric and are evenly spaced from each other along a circumferential direction thereof. A narrow gap 90 is defined between two adjacent arc-shaped portions 424 of the claws. Stator coils 44 surround the linear-shaped portions 422 of the claws to establish an alternating magnetic field. A PCB 46 (printed circuit board) with electronic components mounted thereon is electrically connected with the stator coils 44 to control electrical current flowing through the coils 44. To avoid the coils 44 from coming into electrical contact with the stator core 42, upper and lower insulating frames 48 are used to cover the stator core 42 and electrically insulate the stator coils 44 from the stator core 42.

The balancing structure 100 includes four column-shaped poles 102 extending upwardly from the PCB 46. In this embodiment, the poles 102 are fixedly connected to the PCB 46 through soldering. Alternatively, the poles 102 and the PCB 46 can be assembled by interference fit, and in this situation, a plurality of mounting holes can be defined in the PCB 46 receiving the poles 102 therein. The poles 102 are arranged corresponding to the gaps 90 of the stator core 42. Each pole 102 extends through a corresponding gap 90, and thus the poles 102 and the arc-shaped portions 424 of the claws are concentric and are arranged in alternating fashion along the circumferential direction thereof. A top edge of each pole 102 is approximately at the same level as that of the stator core 42. The poles 102 are made of magnetizable materials, such as steel, iron, iron alloy, nickel, silicon steel, permalloy or ferrite, and thus can magnetically attract the magnet 28 of the rotor 20 to pull the rotor 20 downwardly along the axial direction. In addition, the poles 102 are connected to the PCB 46 and thus can absorb the heat generated by the circuitry of the PCB 46 and the electronic components mounted on the PCB 46. It is to be understood that the poles 102 are used to attract the magnet 28, and thus the shape, the position, the number are not limited to the preferred embodiment as discussed above. For example, the poles 102 can have a cross section being square, triangular, polygonal or irregular. For increasing the magnetic attraction force between the magnet 28 and the poles 102, a size of the poles 102 should be large, and a distance between the magnet 28 and the poles 102 should be small. On the other hand, for avoiding the poles 102 from scraping the hub 22, a height of the poles 102 should not be higher than the stator 40.

When assembled, the stator 40 is mounted around the central tube 1 4. The two bearings 30 are respectively received in the recesses 1 42 of the central tube 1 4. The shaft 24 of the rotor 20 extends through the top bearing 30, the central hole 140 of the central tube 14, and then the bottom bearing 30 into the bottom recess 142 of the central tube 14. The notch (not labeled) near the free end 240 of the shaft 24 is located under the bottom bearing 30. A locking washer 60 is located under the bottom bearing 30 and is engaged in the notch of the shaft 24, thus limiting movement of the shaft 24 along an axial direction thereof. The locking washer 60 defines an inner hole (not labeled) with a diameter smaller than the diameter of the shaft 24, but larger than the diameter of the portion of the shaft 24 defining the notch. A conical-shaped coil spring 50 is arranged between the top bearing 30 and the shaft seat 220 of the hub 22 for providing the top bearing 30 and the hub 22 with a cushion therebetween, thus ensuring that the shaft seat 220 of the hub 22 will not have a severe collision with the top bearing 30 when the cooling fan is activated or transported. A bottom end of the spring 50 abutting against the inner ring of the top bearing 30 has a diameter relatively smaller than that of a top end of the spring 50 abutting against the shaft seat 220. The magnet 28 is positioned around the stator 40 and faces towards the stator core 42.

During operation, the rotor 20 is driven to rotate by the interaction of the alternating magnetic field established by the stator 40 and the magnetic field of the rotor 20. When rotation of the rotor 20 generating an external pressure pulls the rotor 20 upwardly along the axial direction thereof, the balancing structure 100 can magnetically attract the magnet 28 of the rotor 20 and pull the rotor 20 downwardly along the axial direction. Thus the axially upward movement and possible floating of the rotor 20 during rotation of the cooling fan is avoided, and thus the problem of the noise generated by the floating of the rotor 20 during an unstable period of the floating of the rotor 20 can be solved by the present invention.

It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present example and embodiment are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. 

1. A cooling fan comprising: a fan housing having a central tube extending upwardly therefrom; a bearing received in the central tube; a rotor comprising a hub, a magnet fixed to an inner side of the hub, and a shaft extending from a central portion of the hub into the bearing; a stator mounted around the central tube, comprising a stator core having a circular shaped main body and a plurality of claws extending radially and outwardly from the main body, coils being wound on the claws, and a printed circuit board being electrically connected to the coils; and at least one balancing structure extending from the printed circuit board corresponding to a position between two adjacent claws of the stator core, the at least one balancing structure being made of magnetizable material and exerting a downwardly attractive, magnetic force on the magnet of the rotor, whereby the shaft is pulled downwardly by the at least one balancing structure.
 2. The cooling fan of claim 1, wherein the at least one balancing structure comprises a plurality of poles each arranged between a respective pair of adjacent claws.
 3. The cooling fan of claim 1, wherein the stator core has four claws, and the at least one balancing structure comprises four poles arranged between the claws.
 4. The cooling fan of claim 1, wherein each claw comprises a linear-shaped portion extending from the main body and an arc-shaped portion formed at an outer end of the linear-shaped portion, the arc-shaped portions being concentric, a gap being defined between two adjacent arc-shaped portions, the at least one balancing structure being located corresponding to the gap.
 5. The cooling fan of claim 1, wherein the at least one balancing structure is not higher than the stator.
 6. The cooling fan of claim 1, wherein the at least one balancing structure has a cross section being one of the following shape: circular, square, triangular, polygonal or irregular.
 7. The cooling fan of claim 1, wherein the at least one balancing structure is made of one of the following materials: steel, iron, iron alloy, nickel, silicon steel, permalloy and ferrite.
 8. The cooling fan of claim 1, wherein the at least one balancing structure comprises a plurality of poles being arranged between the claws, the poles being symmetrical to an axis of the stator.
 9. The cooling fan of claim 1, wherein the at least one balancing structure is fixedly connected to the printed circuit board by soldering or interference fit.
 10. The cooling fan of claim 1, wherein a shaft seat is formed at the central portion of the hub receiving one end of the shaft therein, and the bearing comprises a pair of ball bearings arranged at two opposite ends of the central tube, a conical-shaped coil spring being arranged between top one of the bearings and the shaft seat, a bottom end of the spring abutting against the top one of the bearings and having a diameter relatively smaller than that of a top end of the spring abutting against the shaft seat.
 11. A cooling fan comprising: a fan housing having a central tube extending upwardly from a base of the fan housing; a bearing fixedly received in the central tube; a stator mounted around the central tube, the stator having a printed circuit board and a plurality of magnetizable poles on the printed circuit board; and a rotor having a hub, a magnet attached to the hub, and a shaft extending from the hub through the bearing in the central tube; wherein the magnetizable poles of the stator interact with the magnet of the rotor to force the magnet and thus the shaft of the rotor to have a tendency to move downwardly.
 12. The cooling fan of claim 11, wherein the stator has a stator core comprising a plurality of claws extending radially and outwardly from a central main body of the stator core, the magnetizable poles of the stator each being located between two neighboring claws. 